The overall goal of this proposal is to develop and bring to human clinical testing a vaccine which induces antibodies that potently and broadly neutralized primary HIV isolates. An effective antiviral antibody response is a desirable feature of prophylactic HIV vaccine to supplement broadly active cellular immune responses as part of a multi-component vaccine strategy. Our vaccine concept is to create oligomeric HIV envelope glycoprotein (env) complexes that provide authentic antigenic mimics of virus-associated env. Although this has been a long-standing goal of HIV vaccine research, authentic oligomers have never been produced as recombinant proteins due to the inherent instability of the non-covalent interaction between gp120 and gp41. However, recent findings in our laboratories demonstrate that this limitation can be overcome by introducing a disulfide bond between the two subunit proteins. As we describe below (and in the Binley et al. Manuscript included in the Appendix), when the introduced cysteine residues are placed in favorable locations, gp120 and gp41 form a stable oligomeric complex whose pattern of antibody reactivity mirrors that of virus- associated env. By stably presenting this antigenically relevant structure to the immune system, this immunogen could in principle induce a neutralizing antibody response superior to that elicited by prior generation env-based vaccines or by natural infection. Our primary approach is to develop a recombinant oligomeric HIV subunit vaccine based on this concept. At present, subunit vaccines provide the most effective means of inducing robust humoral immune responses by delivering the immunogen in a homogeneous, concentrated, and optimally adjuvanted form. However, we recognize that other approaches may provide superior means of delivering the oligomers to the human system. Therefore, we will also examine a nucleic acid-based vaccine approach wherein the oligomers are synthesized in vivo. For this, we have teamed with AlphaVax, Inc. who have developed non- replicating viral vectors based on the Venezuelan Equine Encephalitis (VEE) virus. Although our primary goal is to induce an effective antiviral antibody response, we will also examine cellular immune response elicited by both the subunit and viral vaccines to guide our selection of the optimum construct(s) for further development. Our projects includes an extensive and iterative program for designing and testing these novel immunogens in the best available in vitro and animal models of HIV infection, including the SHIV-macaque model. We seek to develop a safe and efficacious vaccine against HIV for worldwide use in stemming the AIDS epidemic. Therefore, a primary and early focus of our effort will be to prepare vaccine candidates based on envs derived from subtype C viruses. The most promising vaccine candidates will be tested in Phase I/II human clinical trials in both South African and the U.S. Our focused, development-based approach will be carried out by a consortia of distinguished investigators from both industry with experience in all aspects of vaccine design, development and clinical testing.